1. Field of the Invention
The present invention relates to a data reading apparatus. More particularly, the present invention relates to a hologram media reading apparatus.
2. Description of Related Art
With development of storage technique, a compact disc (CD) using such technique may have advantages of large storage capacity, easy preservation, long duration of preservation, low cost and non-easiness of damage of data, etc., and data stored within the CD may be easily read via a CD-ROM. Generally, a read and write method of the CD is to focus a laser light on the CD via an objective lens, so as to perform the read and write operation, and a storage capacity of the CD is determined based on an area size of the CD. In case the area size of the CD is fixed, if the storage capacity thereof is required to be further increased, a recording density of the CD has to be improved, or a wavelength of the laser light has to be shortened. However, limited by a physical limitation of diffraction limit, increasing of the storage capacity of the CD is bottlenecked.
To solve the above problem, hologram CDs and near-field optic CDs developed based on a hologram technique and a near-field optic technique are provided, so as to greatly increase the storage capacity. Since the storage capacity of the hologram CD may be one terabytes (TBs) or more, and a reading speed of the hologram CD via a hologram CD-ROM is more than 100 megabytes (MBs) per second, a combination of the hologram CD and the hologram CD-ROM then becomes a most potential super-capacity data storage solution.
A U.S. Pat. No. 7,167,286 (which is referred to as patent '286 hereinafter) discloses a hologram read and write apparatus shown in FIG. 3 thereof. When data stored on a hologram medium is read via such hologram read and write apparatus, after a reference light beam passes through a hologram on the hologram medium, a part of the reference light beam may pass through an aperture stop, i.e. a filter block shown in FIG. 4 of the patent '286. The aperture stop has a real aperture, so that the reference light beam projected on the real aperture may pass therethrough and may be transmitted to an optical detector. On the other hand, the reference light beam projected outside the real aperture is shielded. When the reference light beam is projected on the hologram medium, it may strike a plurality of holograms overlapping one another. By shielding a part of the reference light beam via the aperture stop, the reference light beam projected to the optical detector may carry data of only one of the holograms, and data of other holograms may be filtered out.
However, since light transmittance on the edge of the real aperture may be varied sharply, an obvious diffraction effect may be generated when the reference light beam passes through the real aperture, which may lead to an inter-pixel interference. Accordingly, an error rate for reading the data from the hologram medium is increased.